idle issues with new A500 behind a fresh 318

600 rpm is a huge drop going into gear, no matter what the idle timing is. I would suspect an issue with the trans.
Not necessarily, If he's running an MP electronic ignition it's pretty common.... The mechanical advance springs are so light it brings in advance at idle... So when you drop it in gear it's not the load that causes the engine to die, the load causes a slight drop in rpms that slowing of the engine is enough that some timing falls out, as the timing falls out the rpms drop further causing more timing to fall out... Next thing that happens is the engine stalls...